Primary care physicians commonly encounter women with acute urinary symptoms, and an estimated $600 million in annual health care expenditures result from diagnosis and treatment of these infections. Nevertheless, little attention has been directed toward development of cost-effective management strategies for these patients, about half of whom have acute cystitis and half of whom have the acute urethral syndrome (AUS). Recent studies have shown single-dose antimicrobial therapy (SDT) to be an effective, safe and less expensive alternative to conventional seven-day treatment for acute cystitis in selected women with antimicrobial-sensitive organisms and negative antibody-coated bacteria (ACB) assays. We have also completed studies demonstrating that E. coli causes most cases of the acute urethral syndrome and that antibiotic therapy is effective for these women. However, prior to widespread use of SDT, critical evaluation of its efficacy, risks, side effects and costs in unselected women with lower tract infection must be completed. These women comprise a heterogeneous group, including those with cystitis and a negative ACB assay; those with cystitis and a positive ACB assay; those with AUS due to low-count coliform infection, and those with AUS due to Chlamydia trachomatis. To date, most published trials of SDT have included only women with cystitis and a negative ACB assay. We propose a prospective, randomized, double-blind, controlled trial comparing the efficacy and cost-effectiveness of single-dose and seven-day trimethoprim-sulfamethoxazole in unselected women presenting to a family medicine clinic with acute urinary symptoms and no evidence of vaginal infection. This project will be done at the University of Washington Family Medical Center, which has a large and well-described patient population. Unique features include: (1) use of SDT in unselected women with acute urinary infection; (2) first use of SDT for women with AUS; (3) extensive microbiologic investigation to determine both etiology of dysuria and precise site of infection in each patient; (4) simultaneous cost-effectiveness analysis of use of SDT in an unselected population; and (5) development of the most cost-effective management strategies for dysuria.